The proposed studies will examine the role of lingual and labial structures and mouth postures on the development and treatment of dento-facial anomalies. In study 1, a longitudinal research design will be employed. The resting mouth posture of 200 children (ages 5-6) will be monitored while they are working independently during a study period at school. A number of dento-facial, skeletal, airway, and oral facial muscle measures will also be obtained on each child. Assessments will be conducted annually for five years. This study is designed to determine the developmental impact of resting mouth and tongue postures on dento-facial development. It is predicted that at the initial assessment youngsters who display inappropriate postures will not differ on dental and skeletal measures from children who exhibit appropriate postures. However the negative influence of these behaviors will be visible across time. In particular, it is predicted that inappropriate mouth and tongue postures will be associated with an increased frequency and severity of dento-facial anomalies. Study two will examine the effect of treating inappropriate resting mouth and tongue postures on the rate of orthodontic correction and the maintenance of orthodontic treatment gains. Using a 2 X 2 factorial design, 80 children (8-13 years) about to begin orthodontic treatment will serve as subjects. Within the total sample, a subsample of 40 children will be identified by their displaying inappropriate resting mouth postures (OMP) (e.g. lips parted and low forward tongue position). The remaining youngsters will exhibit appropriate resting mouth and tongue postures (No-OMP). The OMP children will then be randomly assigned to either an oral muscle therapy or no muscle therapy condition. Similarly, the No-OMP youngsters will be randomly assigned to these same conditions. Youngsters in all conditions will also be exposed to a behavior management procedure designed to facilitate compliance with the orthodontic and/or oral muscle therapy regimens. The compliance procedure is included in order to reduce the likelihood that post treatment differences are a result of compliance problems. It is expected that the correction of inappropriate mouth and tongue postures will increase the rate of orthodontic treatment response, and that this intervention will also be associated with a reduction of retention and relapse problems.